The leader of Cambodia’s main opposition partyhas been released on bail, one year after he was jailed on politically motivated treason charges.

The sudden arrest last September of Kem Sokha from the Cambodia National Rescue Party marked the beginning of a brutal crackdown by the Cambodian prime minister, Hun Sen. Shortly after Kem Sokha’s arrest the CNRP was dissolved by the courts and hundreds of its members forced to flee the country.

A government spokesman said on Monday: “He was released on bail and he is under monitoring by the court.”

Kem Sokha has spent the last 12 months in pre-trial detention in a remote border prison, with his health steadily declining. His daughter, Kem Monovithya, said on Monday her 65-year-old father, who has diabetes, had now been placed under house arrest and was in poor health and needed medical attention. “He has high blood sugar and he needs a long overdue surgery on his left shoulder,” she said.

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It has been seen as a calculated move to appease foreign criticism of the election and ease mounting international pressure on Cambodia. Kem Sokha is the most high profile release so far, following on from fourteen government critics who were freed from jail last month, including environmental activist Tep Vanny.

Phil Robertson, deputy Asia director of Human Rights Watch, cautioned against seeing this as a step forward for Cambodia, and said the release was mainly due to concerns about Kem Sokha’s ill health in prison.

“He should never have been arrested in the first place,” said Robertson. “The ‘colour revolution’ Sokha is accused of leading is a myth, created by the ruling Cambodia People’s Party [CPP] to justify its plan to dissolve the opposition political party, crack down on civil society, and triumph in a sham election.”

Robertson said the “bogus charges against him still stand, and he must appear in court whenever prosecutors snap their fingers”. Kem Sokha still faces up to 30 years in prison for charges of conspiring with the US.

Charles Santiago, spokesman for the Asean Parliamentarians for Human Rights, said the release of Kem Sokha was “far from all that is required”. He said: “Whilst there remains only one political party in parliament and no viable opposition, and until free and fair elections are held, the international community must continue to see this government for what it is: a dictatorship.”

Supporters of Kem Sokha gathered at his home on Monday morning when news of his release broke.

The United Nations and several western countries have widely criticised the general election in July as rigged due to the lack of a credible opposition and the coercion of voters to vote for the CPP. The CNRP, which had 118 of its members banned from politics for five years after the party’s dissolution, has called the July election a farce.

Despite the recent spate of releases, the crackdown on journalists and critics has continued in Cambodia. Last month, Australian film-maker James Ricketson was sentenced to six years in jail after being found guilty of espionage in Cambodia. Prosecutors said Ricketson used journalism as a front for spying, citing links to the CNRP.